A comprehensive assessment of catecholamine physiology during the perinatal period will be conducted using the chronically catheterized fetal sheep and newborn lamb models. These models will be used to study the production, secretion and selected metabolism of catecholamines. Baseline blood levels and the release of catecholamines in response to cellular hypoglycemic stress will be studied at various gestational ages. Particular attention will be directed to the effect of fetal adrenal cortical maturation on catecholamine production and secretion; these studies will be carried out by infusing ACTH, prolactin and cortisol to define which of these agents influences the maturational changes in fetal catecholamine secretory capacity. In addition there are various cardiovascular and endocrine changes which occur at birth which are thought to be secondary to the release of catecholamines. These interrelated homeostatic mechanisms will be evaluated by studying the effect of umbilical cord cutting on catecholamine release, TSH release, triiodothyronine (T3) production, and thermogenesis during the neonatal period. Finally, the interaction of maternal and fetal catecholamine physiology at various gestational ages will be studied using three models. Maternal and fetal release of catecholamines will be studied utilizing maternal exercise as a stimulus. Fetal catecholamine release will be studied by ligating a single umbilical artery, which reduces a portion of the effective placental circulation. A third model will be used which will selectively reduce uterine blood flow to the utero-placental-fetal unit with major maternal cardiovascular or respiratory alterations. These three models will allow us to study the role of maternal cardiorespiratory, fetal-placental and utero-placental alterations in the release of catecholamines in the mother and/or fetus.